gnuplot post-install : exit code 1

[Fergus Daly]

Both cygwin32 and cygwin64, both up-to-date:
Following recent update to gnuplot I'm getting post-install errors
as follows in both setup logs:
running: D:\cygwin..\bin\bash.exe --norc --noprofile "/etc/postinstall/gnuplot.sh"
abnormal exit: exit code=1
My installed.db shows 
gnuplot-X11 gnuplot-X11-5.4.1-1.tar.bz2 1
gnuplot-base gnuplot-base-5.4.1-1.tar.bz2 0
for both 32 and 64 bit setups.
Previously to this update, no such messages.
Any ideas?